This achievement/trophy is awarded to you for completing all of the challenges in the game and then defeating the final Ancestor boss fight on Regular difficulty or higher. See the video: Cheat Video Cheat Video

Always Hard (30G) - Kill the final Ancestor with a relic active in Hardcore difficulty
Eggstra Nemesis! (20G) - Complete the Egg-Stra XP challenge and then activate a generator in the Nemesis DLC package
Hat Trick (20G) - Kill 3 aliens with a single shot from the NX-1 Disruptor in Regular or Hardcore difficulty
Mass Exodus (30G) - Complete the final Ancestor encounter in Regular or Hardcore difficulty
Nemesis Completionist (30G) - Complete every challenge and the final Ancestor encounter in Regular or Hardcore difficulty
Postmaster (20G) - Complete any outpost by activating all of the generators in Regular or Hardcore difficulty
The Final Chapter (20G) - Find all 7 story related intel files in Exodus
Timing is Everything (30G) - Kill the final 3 Ancestors within 10 seconds of killing the first Ancestor in Regular or Hardcore difficulty
Unstoppable (30G) - Complete the final Ancestor with at least 1 relic in Regular or Hardcore difficulty
You Wish (20G) - Hit an Ancestor with a Hypno Knife in Regular or Hardcore difficulty

You can choose to bypass most of the enemies and be stealthy, or you can attack them with Riley to get this achievement/trophy. Attacking with Riley is done in a couple of different ways. You can just get close to an enemy with him and he will automatically attack. You can also initiate an attack by pressing the left bumper on all consoles.

This achievement/trophy has a misleading description because it seems like you just have to destroy 80 containers total throughout the entire campaign. This is not the case, however. This actually has to be done on the Birds of Prey mission while you are controlling the Apache helicopter.

The roofs of buildings have these fuel canisters. They are small and red or big and white. Use missiles liberally to blow up as much as possible.

In the mission Federation Day, there is a part where you are rappelling down and look up at the top of the building. Debris will be falling from the top. One of these items will be a photocopier. Simply let it hit you and kill you to get this achievement/trophy.

In the mission End of the Line, the beginning of the mission is all about remaining stealthy. Just kill the first five enemies that you encounter in a stealthy manner and you will be fine. The only reason you shouldn't get this one is if one of your squadmates kills an enemy before you get the chance to even do so.

Here is a list of all the challenges in Extinction. When there are two numbers listed in the description for a challenge, the first, smaller number is the number that you need to reach when playing solo, and the second number is the number you need to reach when playing in co-op:

-Use only melee attacks to damage aliens until the hive is destroyed
-Do not take any damage from aliens before the hive is destroyed
-Kill 15/25 aliens using pistols before the hive is destroyed
-Find and kill the Leper in 30 seconds
-Kill 15/25 aliens using shotguns before the hive is destroyed
-Kill 15/25 aliens using SMGs before the hive is destroyed
-Kill 15/25 aliens using assault rifles before the hive is destroyed
-Kill 15/25 aliens using LMGs before the hive is destroyed
-Kill 15/25 aliens using sniper rifles before the hive is destroyed
-Spend $$$ before the hive is destroyed
-Kill 5 aliens while they are in the air before the hive is destroyed
-Kill 10 aliens with turrets before the hive is destroyed
-Kill a scorpion with a melee before the hive is destroyed
-Protect a random player from entering last stand
-Do not bleed out before the hive is destroyed
-Do not go into last stand before the hive is destroyed
-Do not let the drill go below 50 health before the hive is destroyed
-Keep shot accuracy at 75% or above before the hive is destroyed
-Keep shot accuracy at 50% or above before the hive is destroyed
-Kill 10 aliens with traps before the hive is destroyed
-Do not take any damage from exploding Seeker Aliens until the hive is destroyed

This is done in the mission Into the Deep. Using the torpedo, you have to direct it to the lower part of the ship and send it into the part of the ship is highlighted in red. A direct hit on that area of the ship is required for this one.

On the mission Clockwork, at the end of the mission, you will drive across some frozen lakes with enemies chasing after you. Using the grenade turret on the vehicle that you're on, shoot at the ice in front of the vehicles chasing you to make them fall into the holes.

In the mission Severed Ties, you will be controlling a tank for the first segment of the mission. Helicopters will attack, and then the NPCs will tell you how to switch to guided missiles. Do that and then use the guided missiles to take out all of the enemy helicopters in the area.

In the mission Atlas Falls, you are tasked with making sure the water pressure stays steady while Merrick screws with the pressure valves. To do this, manipulate the meters on the screen with the left stick to raise and lower them in an attempt to keep the meters in the middle of the screen. You're doing good when the meter is green, not so good when it is yellow, and are about to lose when it is red.

Storm the common room and kill everyone without taking damage on Veteran.

In the mission Atlas Falls, there is a point where you go to breach a door, only for the enemies to start shooting through the door instead. You basically have to clear that room without taking any damage. The best way to do this is to just blindly throw frags and flashbangs into that room from a safe angle, then slowly pushing your way in and taking out the stragglers.

Safeguard is one of the game modes in Squads. It is basically Horde Mode. It ends when you reach round 20, so just win a game of Safeguard, basically. This can also be achieved by playing Safeguard in co-op and on any difficulty setting.

In the mission Federation Day, during the part when you are rappelling down the building and facing the street, you are tasked with killing enemies on balconies below. After killing the first two enemies as instructed by the squad, you should be able to see this enemy sleeping in a chair on a different balcony. Take him out with a gunshot.

Reach the exfil chopper with 1 minute and 30 seconds or more remaining on the clock.

When you beat Extinction, the goal is to reach the exfiltration helicopter to officially escape. There is a lime limit, and you need to get to the chopper, so to speak, with at least 1:30 remaining on the clock.

In the mission called Loki, you get control of a satellite that can fire missiles at precise locations. You are tasked with killing enemy forces using this weaponry. You will be able to tell the blast radius of the missiles based on the yellow outline. The blue colored blips during this mission will be your allies, so make sure no blue colors overlap into the yellow radius when firing the missiles.

Basically, after beating Extinction Mode for the first time, you can go back through and beat it again, except you can choose to add a Relic to your game to make it more difficult. This is like the "Skulls" from the Halo series. Just beat Extinction again, but this time with a Relic activated to make it more challenging for you.